Familiar to those skilled in the utility furnace art, the coal pulverizing bowl mill remains a huge, noisy, exotic unit of machinery gulping down a continuous supply of coal and delivering it pulverized to the waiting burners of the furnace. These mills are characterized by a rotating table upon which the coal is directed into the journal rolls which bear down upon the table and reduce the coal to a specified mesh size. The coal, pulverized between the journal rolls and upper surface of the table, is discharged over the outer periphery of the table where warm air is supplied to dry the coal and entrain it for conveyance upward through the separator housing. Veins are mounted beyond the periphery of the table to guide the air-entrained coal, returning the larger sizes to the table and sweeping properly sized coal particles into discharge conduits, allowing the fuel to be delivered to the furnace burners. The journal rolls are supported within the volume of the dome formed by the separator housing above the table.
The mechanical wear on the table and rollers is one of the primary concerns of those skilled in this art. Despite admirable advances in materials and structural arrangements, the journal rolls supported by the separator housing framework must be periodically removed for service, repair, and even replacement, through access doors provided in the wall of the separator housing for each journal roll. In the past, a permanent craneway was provided with which to jockey each journal roll and its mounting fixtures out of the access door for removal to an area where service, repair, and replacemnt are performed.
The problem of removing and replacing journal rolls is raised to monumental proportions by the limited access to the mill. Each unit of equipment essential to the furnace operation is necessarily positioned close to the mill. The mill is nested in this technological tangle of equipment and connecting conduits, leaving only enough floor space to get a mobile crane conveyance to a single position in front of the mill. Thus, the permanent overhead craneway, in the order of 40 tons of structural steel, has been required to reach the journal rolls through their access doors spaced around the wall of the separator housing. If a mobile crane can have the journal rolls brought to it at a single available station, the craneway could be eliminated with a savings of significant magnitude.
Rather than attacking the problem of access by rearranging the units surrounding the mill to provide multiple pathways to the mobile crane, a solution is seen in redesigning the mill, itself, to bring the journal rolls to the single station already available.